The structure and dielectric properties of rare earth niobate compounds within the Ln3NbO7 (Ln = Nd, Gd, Dy, Er, Yb and Y) and Ln2
(Ln',Nb)O7 (Ln = Nd, Sm and Ln' = Yb) series are investigated. The crystal structure of the all the studied materials is found to be fluorite-related including webertite-type, pyrochlore, and defect fluorite structures. It is observed that the relative permittivity of the defect fluorite Ln3NbO7
(Ln = Dy, Er, Yb and Y) increases with the increase in temperature and exhibits low dielectric loss up to approximately 350 K. Above 350 K, the dielectric loss increases rapidly with increasing temperature as the onset of electrical conductivity takes place. Of particular interests are Gd3NbO7
, which exhibit a frequency and temperature dependent dielectric relaxation behavior. At 1 MHz Gd3NbO7
reaches its maximum relative permittivity of ∼34 at about 330K, while at the same frequency, the maximum relative permittivity of Nd3
NbO7 is attained at about 500 K. By contrast, Nd2
(Yb,Nb)O7 and Sm2(Yb,Nb)O7, which crystallize in a pyrochlore-type structure, do not show dielectric relaxation and, comparatively, exhibit a more temperature-stable dielectric permittivity response.